Media converter systems are used in data networks to convert signal transmission from one media, such as twisted pair copper, to another media such as fiber optics. Media converter systems include a power supply and one or more media converters. The media converter performs the conversion of signal transmission. Media converters receive the data signal through one media and output the data signal through another. The media converter is an active device and requires a supply voltage.
A power supply is used to provide operating voltage to the media converters in a media converter system. As shown in FIG. 1, conventional power distribution systems utilize a centralized power supply. A standard voltage V.sub.in is provided to a central power supply 102 at input 104. V.sub.in is typically an AC voltage such as the 60 Hz 115 volt (VAC) standard but can be other voltages or even DC. The media converter operates on 5 volts DC (VDC). Therefore, the standard line voltage V.sub.in must be converted before being applied to the downstream media converter. The centralized power supply 102 converts V.sub.in into a usable voltage and provides several DC outputs 106, 108, and 110 that may be different. The output voltages are fed or bussed to downstream devices such as media converters.
Centralized power distribution systems suffer from several drawbacks. Because V.sub.in must be converted to the usable voltage before transmission, the current supplied from the power supply through the transmission lines is the total current consumption used by all of the downstream devices which is inefficient because of I.sup.2 R losses. The transmission lines must be selected so that the maximum current rating is not exceeded, and this leads to a lack of system flexibility.
Also, governmental certification requirements require that the downstream devices be at or below a certain voltage to be classified as a low voltage device not subject to UL/CSA safety testing. Avoiding a non-low voltage rating allows the device to be much cheaper. If the device is configured to operate at a relatively high voltage that allows low current transmission, the device may not be classifiable as a low voltage device and will become more expensive as a result.
Also, because V.sub.in is converted directly to the usable voltage by the centralized power supply, if downstream devices require differing voltages, then the centralized power supply must have multiple outputs supplying the differing voltages as shown in FIG. 1. Power supply complexity is increased to provide the differing voltages, and flexibility of the system is decreased because downstream devices requiring voltages other than that provided by the power supply cannot be easily added.
If many devices are linked to the centralized power supply and its current sourcing limits have been reached, redundancy cannot be added to provide a greater current sourcing limit without adding another centralized power supply and routing its outputs to some of the downstream devices previously linked to the initial power supply. This inability to be made redundant also poses a problem when the initial power supply fails. Because there is no redundancy, no back up power is available to instantaneously handle the current demand previously addressed by the initial power supply.
Furthermore, in some centralized power supply systems, the centralized power supply outputs an AC voltage or the AC line voltage is simply distributed to power supplies at the downstream devices. In systems where the informational signals must be transmitted in proximity to the power transmission lines, the AC voltage in the transmission lines may introduce unwanted characteristics into the informational signal. Therefore, in such centralized power supply systems, the transmission lines must be isolated from the informational signals.